Gaseous fuel engines are known for their ability to burn clean relative to their compression ignition engine counterparts. However, gaseous fuels are well known for the difficulty in attaining successful ignition. Some gaseous fuel engines utilize a spark plug, whereas other engines are known for utilizing a small amount of distillate diesel fuel that is compression ignited to in turn ignite a larger charge of gaseous fuel. In these engines, the gaseous fuel may be supplied to the engine intake manifold or metered directly into individual cylinders where it is mixed with air prior to being ignited responsive to the pilot diesel injection near top dead center.
U.S. Pat. No. 6,298,833 teaches a dual fuel injector with the ability to directly inject both gaseous and liquid fuels into an engine cylinder. The reference teaches a dual concentric nozzle check design where liquid diesel fuel is injected through a small inner set of orifices through the outer needle and the gaseous fuel is injected through a concentric set of gaseous fuel outlets through a tip component. Recognizing that gaseous fuel has low viscosity and may be unsuitable to lubricate the moving gaseous needle valve member and to inhibit migration of gaseous fuel into the liquid fuel, this reference teaches a fluid sealing strategy in which an annular volume of pressurized liquid fuel surrounds the guide segment of the gaseous needle valve member. The liquid fuel sealing pressure is maintained equal to or slightly greater than the pressure of the gaseous fuels. While this reference may teach an effective strategy for inhibiting leakage of gaseous fuel into the liquid fuel within the dual fuel injector, it fails to anticipate problems or teach solutions to potential operational modes of an engine equipped with a dual fueling system that utilizes gaseous and liquid fuels. For instance, there may be instances where the gaseous fuel supply may be exhausted and the engine may need to operate in a so called limp home mode utilizing only the liquid fuel as a fuel source. Such an operational mode may present previously unrecognized problems in the context of dual fuel injection systems that utilize a dual fuel injector to inject both gaseous and liquid fuels.
The present disclosure is directed toward one or more of the problems set forth above.